AD-RI62 882 HULL FORM PARAMETERS FOR IMPROVED SEAKEEPING NREDUCED RESISTANCECU) DAVID N TAYLOR NAVAL SHIPRESEARCH AND DEVELOPMENT CENTER BET

U SIFIED D A WALDEN ET AL AUG 85 F/G 13/1 U

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MICROCOPY RESOLUTION TEST CHART

NATIONAL BU R E

AU OF STANDARDS- 1963-A

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DAVID W. TAYLOR NAVAL SHIPRESEARCH AND DEVELOPMENT CENTER f4SI

Bethes, Maryland 20084

HULL FORM PARAMETERS FOR IMPROVED SEAKEhPING

AND REDUCED RESISTANCE

00N ~by D I

(D David A. Walden ELECand JANO 76

Paul J. Kopp S-APPROVED FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED

0

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0August 1985 DTNSRDC /SPD-1 168-01

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DEPARTMENT

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HULL FORM PARAMETERS FOR IMPROVED SEAKEEPING AND REDUCED RESISTANCE

1: Pt-R'd)%AL At/ THOR(S)David A. Walden and Paul J. Kopp

a 'Y 1- R PORT 13 b TiME COVERED 114 DATE OF REPORT (Year, Month, Day) 15PA GE COUNTFinal IFROM TO 1985 August 15 2S

'In Su;FPiEMNTARY NOTATION

(OSATI CO)S18 SUBJECT TERMS (Continue on reverse if necessary and identifli by block number)

I ' - RO(UP SUB-GiROUP Optimization Resistance ",6___ Frigate Hull Forms

Seakee i ng1 ATH IRA(- r (Continue on reverse if necessary and identify by block number)

L-Thii&results of a study on seakeeping and resistance optimized frigate hull forms arepresented: The seakeeping optimization is based on the work of Walden and Grundmann.Resistance calculations are based on the method of Holtrop. The effects of cost functionweighting factors are discussed.

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Energy R&D OfficePropulsion and Auxiliary Systems DepartmentDavid W. Taylor Naval Ship R&D Center

UNCLASSIFIED. 1 I I,~ L'.

.. . . . . . . .. . . . . . . . .. . . . . . . .

TABLE OF CONTENTS

Page

LIST OF TABLRES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. i

ADISOFTATIE I HTO.. .. .. .. .. .. .. .. .. .. .. . . . . 1 i

NTROTION . .... .. .. .. .. . .. .. .. . .. . o. . *

ABSACRUN.............. . * .. . . . .. .. ... . .1

DESINSPROCEDUE INOMT . . . .. . . . . . . . . . . . . . . . . .2

OPTIMIZATION RESULTS. ......... . . . . . . . . . . . . . . . . . 3

CONCLUSIONS . . . .. .. ... . . . . . . . . . . . . . . . . . . . .

REFERENCES................... . .. .. .. .. o.. .. .. .. .... . . .

LIST OF FIGURES

1- Wave Height Curves .......... . . . . . . . . .. . .. ... .

2 - EPH Curves................. . . . . . . . . . . . . . . .8

3 - Wave Height and EHP versus Water Plane Coefficient Forward .. .. .. . .

4 -Wave Height and EHP versus Water Plane Coefficient Aft . .. .. .. . . 10

5 -Wave Height and 1]HP versus Vertical Prismatic Coefficient Forward . .. 11

6 -Wave Height and EHP versus Vertical Prismatic Coefficient Aft . ... 12

7 20 Knot Seakeeping Ship Hull Form. ....... . .. .. .. .. .. 13

8 20 Knot Resistance Ship Hull Form......................14

9 -20 Knot Combination Ship Hull Form....... ..... o .. .. .. .. .. . . 15

10 - IliP versus Critical Wave Height for All 20 Knot Ships Generated ... 16

-7-

. ; , ,i , .,, -4:4 .-"' .. , i!, r - , , . y r. j- ,- , ' . ,', -.a-i - , . - - -- -

LIST OF TABLES

Page

1 - Hull Form Parameter Ranges . . ........................ 17

2 - Cost Function Weighting Factors . . . . . . . . . . .......... 18

3 - Seakeeping and Resistance Characteristics of Optimum Ships . . . . . . 19

4 -Hull Form Parameters of Optimum Ships ................. 20

-i

,.

i ! %

A

.

._9

i iv

NOTATION -

CM Midship section coefficient

CVPF Vertical prismatic coefficient forward

CYPA Vertical prismatic coefficient aft

CVJPF Waterplane coefficient forward

CWPA Waterplane coefficient aft

L Length

T Draft

v Displacement (m3 )

Accesion ForNTIS CR&OTIC TA13UtianrouncedJ. stification

ByDi.j ibAtiou ......................................

Avalability Codes

Dis Aai

specia

v~

ABSTRACT

The results of a study on seakeeping and resistanceoptimized frigate hull forms are presented. The seakeepingoptimization is based on the work of Walden and Grundmann.Resistance calculations are based on the method of Holtrop.The effects of cost function weighting factors are discussed.

ADMINISTRATIVE INFORMATION

This work was performed by the David Taylor Naval Ship Research and

Development Center (DTNSRDC), Code 1561. Funding was provided by Energy R&D

Office, Code 2759, under Work Unit Number 2759-339.

INTRODUCTION

The objective of this project was to develop a method for designing frigate

hull forms that exhibit superior seakeeping qualities and improved resistance

characteristics. This method can be used in support of the feasibility design of

the FFX.

BACKGROUND

In order to develop hull forms with the desired qualities of good seakeeping

ir•I low resistance, a method of quickly obtaining the ship seakeeping responses and

r,.sistance is needed. Model testing is too costly and time consuming for feasibi-

lity design work. Optimization methods appear to be a useful way to investigate

Vwtriations in hull forms and produce a satisfactory combination of parameters.

volen bind Grundmann discuss the problems with and methods of performing seakeeping

,timization.

The intention was to systematically investigate the seakeeping and resistance

,-rformance of a large number of hull forms in a search for those with a com-

)irvatiori of both good seakeeping and low resistance. The level of detail in the

hiull form description was limited to that typically available at feasibility design

stage. By automating the hull form parameter selection, hull form generation and

performance assessment, it is possible to examine a. very large number of hull

forms.

*A complete listing of references is given on page 5.

-4~: .. . - . - ... % . °. . - . .'. . . - . .. .'. . ' .. '- .' ' . . . ..' -. " '

"'"* " ". ,, ." ". . .. . ,. ,".' " : .. '. ," " . , .' ,'.'-. ...'.. :. ," . - . .. . . . - - . .. .*, . .*

The method must also allow constraints due to requirements other than

seakeeping and resistance to be placed on the hull forms. These can include minimum

draft for sonar immersion, minimum displacement for payload, maximum length to beam

Fratio for structural considerations, etc.P4

DESIGN PROCEDURE

The optimization technique used in this investigation was the same as that

discussed in Reference 1. The same set of motion criteria as well as geometric

constraints were used. The critical wave height, as explained in Reference 1, is

that wave height at which one of the motion criteria (slamming, pitch, or vertical

acceleration at the forward perpendicular) is exceeded. The cost function to be

minimized was modified to allow weighting of the average critical wave height and

the bare hull resistance. The parameters searched as well as the ranges of

variation are shown in Table 1.

In order to determine the bare hull resistance (EHP) for a given set of hull

form parameters, a resistance prediction method based on that described in

Reference 2 was used. This method is based on a regression analysis of model and

full scale test data. The equations are given for the components of the total

resistance, i.e., frictional, wavemaking, appendage, transom, bulbous bow, and

model-ship correlation. For this study, the only components considered were fric-

tional, wavemaking, transom, and correlation resistance.

Three cases were investigated, namely: (i) maximizing the seakeeping perfor-

mance, (ii) maximizing the resistance performance and (iii) maximizing a weighted

combination of both seakeeping and resistance performance. Each of the three cases

was investigated at ship speeds of 10, 20, and 30 knots. Two optimization methods

are used in this study. A modified exponential random search was used to search

for a global minimum of the cost function. The random search results are then used

as the starting point for a direct search optimization, which refines the result.

The optimization methods are discussed in References 1, 3, and 4. This approach of

using the two types of optimization methods allows for a relatively high degree of

certainty in actually finding an "optimum."

The combination case mentioned in the previous paragraph requires further

discussion regarding the cost function. The cost function is specified by

cost (seakeeping weight) x critical wave height + (resistance weight) x EHP

2

cost (seaeepig weght

and has to be minimized during the optimization procedure. The weighting for the

critical wave height and resistance are developed in the same manner, so the

following description for the wave height weighting applies to the resistance

weighting as well. At 10 knots for example, the critical wave height for the

10-knot seakeeping ship is greater than the critical wave height for the 10-knot

resistance ship. The resistance of the seakeeping ship is also greater than that

of the resistance ship. The inverse of the difference between the two wave height

values was used as the wave height weighting for the combination ship at 10 knots

while the inverse of the difference between the two resistance values was used for

the resistance weighting in the cost function. This approach is also used for the

other ship speeds. Such a weighting procedure is required to normalize the

seakeeping performance specified by significant wave height in meters and the

resistance performance given in EHP. By changing these weights, it is possible to

control the relative influence of seakeeping and resistance on the design. It will

be shown that by varying these weights, it is possible to describe a curve of "best

ships" ranging from best seakeeping with little consideration of resistance to best

resistance with a little consideration of seakeeping. These weighting factors are

developed from the results of the random search but are also used as the weights in

the direct search. The weights used are shown in Table 2.

OPTIMIZATION RESULTS

The results of the optimizations are presented in terms of the seakeeping and

resistance characteristics, and the hull form parameters. Table 3 gives the criti-

cal wave heights and the EHP for each of the ships at 10, 20, and 30 knots. Table

4 gives the hull form parameters of the ships in Table 3. Critical wave height

curves are presented in Figure 1 for the seakeeping, resistance, and combination

ships. The EHP curves are presented in Figure 2.

It can be seen from Tables 3 and 4 that the 10- and 20-knot seakeeping ships

are in fact the same ship. This is also true of the 20- and 30-knot resistance

ships. The reason for the two seakeeping ships being identical is that at 10 and

20 knots pitch limits tend to govern while at 30 knots slamming becomes more impor-

tant. Further discussion is givpn in Reference 1. The 20- and 30-knot resistance

ships are the same because at low speeds (10 knot resistance ship), the driving

influence is wetted surface while at the higher speeds, wavemaking dominates.

-- " ; . ... _ . . . . _ , . , , • . _ , . , , - , , .. . ... . . ... .

TW- TZ

Figures 3, 4, 5, and 6 show the trends of critical wave height and EHP versus

CWPF, CWPA, CVPF, and CVPA, respectively. These plots were obtained from the com-

bined set of reasonable ships considered in the seakeeping, resistance, and

combination optimizations. The important point to notice here is that the trends

between each parameter in the figures and EHP and critical wave height are in

general opposite. Better resistance ships tend to have a lower CWPF and CWPA,

while larger values increase the wave height. Similar trends can be observed in

CVp F and CVPA -

Body plans, design waterline curves, and sectional area curves for the 20-knot

ships are given in Figures 7 through 9. Notice that the 20-knot combination ship

has the forebody of the seakeeping ship and the afterbody of the resistance ship.

This is not surprising in light of the information that may be obtained from

Figures 3, 4, 5, and 6. The trend of ElHP with CWPA and CVPA is stronger than that

of the critical wave height. The converse is true for CWPF and CVPF.

Figure 10 shows the EHP plotted against the critical wave height for the com-

bined set of 20-knot ships. The lower left side of the plot is where the optimal

resistance ships are, while on the extreme right side are the optimal wave height

ships. Between these two extremes are the optimal combination ships.

CONCLUSIONS

The combination of a procedure for generating a hull form from a set of coef-

*ficients, a simple seakeeping measure of merit, a resistance estimation procedure,

and an optimization prograi,, nas resulted in a powerful tool for use in early

dos ign.

Future work is needed in improving the resistance estimation procedure,

applying more powerful optimization techniques requiring fewer iterations,

improving the constraints on combinations of hull form parameters to ensure that

all ships considered are "reasonable", and improving the seakeeping criteria used

in calculating the limiting wave heights.

REFERENCES

1. Walden, David A. and Peter Grundmann, "Seakeeping Optimization,"

Report DTNSRDC/SPD-I144-Ol (May 1985).

2. Holtrop, J., "A Statistical Re-Analysis of Resistance and Propulsion

Data," International Shipbuilding Progress, Vol. 31, No. 363 (Nov 1984).

3. Gray, M., "A Survey of Current Optimization Methods," NSRDC Report 3605

(Jan 1971).

4. Parsons, M., "Optimization Methods for Use in Computer Aided Ship Design,"

SNAME, Proceedings of the First Ship Technology and Research (STAR) Symposium,

Washington, D.C. (Aug 1975).

%)

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19 Knot Combinationo 0e Knot Coibination3. -030 Knot Combination

1s 12 14 16 is of 22 24 26 28 30,. Skip S;peed (knots )

Figure I -Wave ieight Curves

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0 - Figure 2 nt EHP Curves

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Ski'+I +Figure 7 - 20 Knot Seakeeping Ship Hull Form

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~Figure 9 - 20 Knot Combination Ship Hull Form

15

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700 X

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3.5 4.0 4.5 5.0 5.5 6.0

WAVE HEIGHT m

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Figure 10 -EHP versus Critical Wave Height forall 20 Knot Ships Generated

16

v v v T v -, T-- I W- I- 7

TABLE 1 - HULL FORM PARAMETER RANGES

Parameter Low High

CWPF 0.40 0.90

CWPA 0.60 1.00

CVp F 0.50 0.90

CVPA 0.35 1.00

T (m) 3.00 7.00

L (m) 90.00 170.00

V (m 3 ) 4300.00 4300.00

cM 0.80 0.8o

17

"CA

TABLE 2 - COST FUNCTION WEIGHTING FACTORS

Wave Height Resistance10 Knots 20 Knots 30 Knots 10 Knots 20 Knots 30 Knots

Seakeeping

10 knots - -- 0

20 knots - -i .... 0 --

30 knots .... 0

Resistance

10 knots 0 --. 1 ...

2o knots - 0 .. 1 __

30 knots 0

Combination

10 knots -0.574 -- 0.019 --

20 knots -- -0.733 -- 0.002 --

30 knots ...- 0.685 .... 0.00005

., . Km~

v" ia

'

TABLE 3 - SEAKEEPING AND RESISTANCE CHARACTEISTICS OF OPTIMUM SHIPS

Wave Height (meters) Resistance (EHP)

10 Knots 20 Knots 30 Knott 10 Knots 20 Knots 30 Knots

Seakeeping

10 knots 6.14 5.61 5.22 473 4400 19900

20 knots 6.14 5.61 5.22 473 4400 19900

30 knots 4.64 5.00 5.57 462 5480 37500

Resistance

10 knots 4.40 3.85 3.60 419 3930 20300

20 knots 4.70 4.25 4.11 432 3760 16900

30 knots 4.70 4.25 4.11 432 3760 16900

Combination

10 knots 5.81 5.22 4.92 443 4130 19300

20 knots 5.71 5.15 4.84 445 3950 17800

30 knots 6.00 5.57 5.37 461 4340 20800

19

TABLE 4 -HULL FORM PARAMETERS OF OPTIMUM SHIPS

Seakeeping Res istance Combination

lWPt o.686 0.498 o.668

CWPA o.965 0.602 0.771

CVPF o.664 0.767 0.677

CVPA 0.470 0.809 0.597

T (in) 4.26 4.23 4.47

L (mn) 149.00 136.88 145.16

*B (in) 14.90 17.11 14.53

20 Knot

VVCWPF o.686 0.462 o.6o6

* WPo.965 0.758 0.776

oVF .664 0.723 o.64o

CVPA 0.470 0.585 0.560

T (in) 4.26 4.76 4.62

L (in) 149.00 145.43 147.70

B (in) 14.90 15.99 15.32

30 KnotCWPF 0.719 0.462 0.735

CWPA o.986 0.758 0.905

CVPF o.674 0.723 0.664

CVPA o.464 0.585 0.487

T (mn) 5.25 4.76 4.55

L (mn) 105.10 145.43 141.34

B (mn) 16.59 15.99 14.38

i

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